The present invention relates to a semiconductor device and, for example, relates to a semiconductor device including a power transistor.
A power transistor is widely used today as an element that passes a current through a load requiring a large current. As the power transistor, an element using a bipolar transistor or an element using MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used, for example. Particularly, IGBT (Insulated Gate Bipolar Transistor) is commonly used.
A device in which a power transistor is used is provided with a circuit that detects an overcurrent in order to prevent breakdown of the device due to short-circuit of a load. For example, by placing a sense transistor smaller than a power transistor in parallel with the power transistor and monitoring a current flowing through the emitter of the sense transistor, it is possible to monitor a current flowing through the power transistor. For example, by placing a shunt resistor on the emitter side of the sense transistor and monitoring a voltage between terminals of the shunt resistor, it is possible to monitor a current flowing through the emitter of the sense transistor.
However, if the shunt resistor is placed, the emitter voltage of the sense transistor differs from the emitter voltage of the power transistor under the effect of the voltage occurring at the shunt resistor. Therefore, a current detection circuit that is formed using the sense transistor and the shunt resistor has a problem that the detection accuracy is low.
In the technique disclosed in Japanese Unexamined Patent Application Publication No. H11-299218, an operational amplifier that virtually short-circuits the emitter of the power transistor and the emitter of the sense transistor is placed in order to solve the above problem. By placing such an operational amplifier, it is possible to substantially equalize the emitter voltage of the power transistor and the emitter voltage of the sense transistor and thereby improve the detection accuracy of the current detection circuit.